Pulse oximetry system with electrical decoupling circuitry

ABSTRACT

A pulse oximetry system for reducing the risk of electric shock to a medical patient can include physiological sensors, at least one of which has a light emitter that can impinge light on body tissue of a living patient and a detector responsive to the light after attenuation by the body tissue. The detector can generate a signal indicative of a physiological characteristic of the living patient. The pulse oximetry system may also include a splitter cable that can connect the physiological sensors to a physiological monitor. The splitter cable may have a plurality of cable sections each including one or more electrical conductors that can interface with one of the physiological sensors. One or more decoupling circuits may be disposed in the splitter cable, which can be in communication with selected ones of the electrical conductors. The one or more decoupling circuits can electrically decouple the physiological sensors.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/436,015, filed May 5, 2009, which claims priority from U.S.Provisional Application No. 61/050,476, filed May 5, 2008, which areboth hereby incorporated by reference in their entireties.

BACKGROUND

Hospitals, nursing homes, and other patient care facilities typicallyinclude patient monitoring devices at one or more bedsides in thefacility. Patient monitoring devices generally include sensors,processing equipment, and displays for obtaining and analyzing a medicalpatient's physiological parameters. Physiological parameters include,for example, respiratory rate, oxygen saturation (SpO₂) level, pulse,and blood pressure, among others. Clinicians, including doctors, nurses,and certain other medical personnel, use the physiological parametersobtained from the medical patient to diagnose illnesses and to prescribetreatments. Clinicians also use the physiological parameters to monitora patient during various clinical situations to determine whether toincrease the level of medical care given to the patient.

Many monitoring devices receive physiological signals from one or moresensors, such as pulse oximetry sensors, acoustic sensors, and the like.Medical cables attached to the sensors transmit signals from the sensorsto the monitoring device.

SUMMARY

Certain implementations of a pulse oximetry system for reducing the riskof electric shock to a medical patient include a plurality ofphysiological sensors, where at least one of the physiological sensorshas a light emitter that can impinge light on body tissue of a livingpatient and a detector responsive to the light after attenuation by thebody tissue. The body tissue can include pulsating blood. The detectorcan generate a signal indicative of a physiological characteristic ofthe living patient. The medical apparatus may also include a splittercable having a monitor connector that can connect to a physiologicalmonitor, a plurality of sensor connectors that can each connect to oneof the physiological sensors, and a plurality of cable sections eachdisposed between a sensor connector and the monitor connector, whereeach of the cable sections have one or more electrical conductors. Theone or more electrical conductors for at least some of the cablesections may include a power line that can supply power to one or moreof the plurality of physiological sensors, a signal line that cantransmit the physiological signals from one or more of the physiologicalsensors to the physiological monitor, and a ground line that can providean electrical return path for the power line. Further, the splittercable may also have one or more decoupling circuits in communicationwith selected ones of the one or more electrical conductors. The one ormore decoupling circuits may communicate physiological signals betweenone or more of the physiological sensors and the physiological monitor.The one or more decoupling circuits can electrically decouple thephysiological sensors, such that the one or more decoupling circuits areconfigured to substantially prevent ground loops from forming in theground line.

In certain embodiments, a medical apparatus for reducing the risk ofelectric shock to a medical patient when used with a pulse oximeterincludes a plurality of physiological sensors. At least one of thephysiological sensors can include a light emitter that can impinge lighton body tissue of a living patient, where the body tissue has pulsatingblood. The physiological sensor can also include a detector responsiveto the light after attenuation by the body tissue, such that thedetector can generate a signal indicative of a physiologicalcharacteristic of the living patient. The medical apparatus may alsoinclude a splitter cable that can connect the plurality of physiologicalsensors to a physiological monitor. The splitter cable may include aplurality of cable sections that each includes one or more electricalconductors that can interface with one of the physiological sensors. Oneor more decoupling circuits can be disposed in the splitter cable. Theone or more decoupling circuits can be in communication with selectedones of the one or more electrical conductors. The one or moredecoupling circuits can communicate physiological signals between one ormore of the physiological sensors and the physiological monitor. The oneor more decoupling circuits can electrically decouple the physiologicalsensors.

Various embodiments of a method for reducing the risk of electric shockto a medical patient as used with a pulse oximeter may include providinga plurality of physiological sensors, where at least one of thephysiological sensors has a light emitter that can impinge light on bodytissue of a medical patient and a detector that can generate a signalindicative of a physiological characteristic of the living patientresponsive to the light after attenuation by the body tissue. The methodcan also include providing a medical cable assembly having one or moreelectrical conductors that can allow communication between the pluralityof physiological sensors and a physiological monitor, such that themedical cable assembly can provide signals representing physiologicalinformation of a medical patient from the plurality of physiologicalsensors to the physiological monitor. Moreover, the method may includeelectrically decoupling the plurality of physiological sensors using oneor more decoupling circuits disposed in the medical cable assembly. Theone or more decoupling circuits may be in communication with theplurality of physiological sensors and with the physiological monitor.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment of the inventionsdisclosed herein. Thus, the inventions disclosed herein may be embodiedor carried out in a manner that achieves or optimizes one advantage orgroup of advantages as taught herein without necessarily achieving otheradvantages as may be taught or suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments will be described hereinafter with reference to theaccompanying drawings. These embodiments are illustrated and describedby example only, and are not intended to limit the scope of thedisclosure. In the drawings, similar elements have similar referencenumerals.

FIG. 1 illustrates a perspective view of an embodiment of aphysiological monitoring system;

FIGS. 2A and 2B illustrate block diagrams of example physiologicalmonitoring systems having splitter cables;

FIG. 3 illustrates a block diagram of another embodiment of aphysiological monitoring system having multiple cables;

FIG. 4 illustrates a block diagram of yet another embodiment of aphysiological monitoring system having multiple cables;

FIGS. 5A through 5C illustrate embodiments of decoupling circuits;

FIG. 6A illustrates a side view of an example splitter cable;

FIG. 6B illustrates a bottom view of the example splitter cable of FIG.6A;

FIG. 7 illustrates a perspective view of an example sensor and cableassembly;

FIGS. 8A and 8B illustrate block diagrams of example cables that includeone or more information elements;

FIG. 8C illustrates an embodiment of a circuit for communicating withone or more information elements and a sensor;

FIG. 9 illustrates a block diagram of exemplary forms of data that canbe stored in an information element;

FIG. 10 illustrates an embodiment of a physiological monitoring systemhaving multiple networked physiological monitors;

FIGS. 11 and 12 illustrate flowchart diagrams of example cablemanagement processes; and

FIGS. 13 and 14 illustrate flowchart diagrams of example patient contextmanagement processes.

DETAILED DESCRIPTION

Multiple sensors are often applied to a medical patient to providephysiological information about the patient to a physiological monitor.Some sensors, including certain optical and acoustic sensors, interfacewith the monitor using a cable having power, signal, and ground lines orwires. One or more these lines can pose an electric shock hazard whenmultiple sensors are attached to the patient. If an electrical potentialexists in the ground line, for instance, a ground loop can form in thepatient or in the ground line, allowing unwanted current to pass throughthe patient through the ground line. Power fluctuations or surges, suchas from a defibrillator, can potentially harm the patient and damage themonitor or the sensors.

This disclosure describes decoupling circuitry that can be used toprevent or substantially prevent ground loops and other current loopsfrom forming. Using decoupling circuitry in this manner can be referredto as providing sensor isolation, patient isolation, patient protection,sensor decoupling, or the like. Currently-available physiologicalmonitors that connect to one sensor at a time using a single cable maynot have this decoupling circuitry. Upgrading these monitors to receivetwo or more sensors can create the shock hazard described above unlessprotective circuitry is added to these monitors. For existingsingle-sensor monitors, adding this circuitry might require a costlyupgrade of the monitors' internal components. For new single-sensormonitors, the decoupling circuitry could be added during manufacturing.But this approach would be cost-inefficient for buyers who wish to useonly one sensor with the device.

Accordingly, in certain embodiments, the decoupling circuitry isprovided in a medical cable assembly. The medical cable assemblyincludes, in some embodiments, a splitter cable that interfaces multiplephysiological sensors with a single sensor port on a physiologicalmonitor. Advantageously, in certain embodiments, the medical cableassembly allows multiple sensors to connect to a monitor while reducingthe risk of electric shock to a patient.

Turning to FIG. 1, an embodiment of a physiological monitoring system100 for monitoring a medical patient is shown. The physiologicalmonitoring system 100 includes a physiological monitor 110 coupled witha sensor assembly 150 through a cable 130. The monitor 110 includesvarious visual indicia and user controls 105 for displaying sensorparameters, alarms, and the like and for receiving user input. Thesensor assembly 150 could include any of a variety of physiologicalsensors. For example, the sensor assembly 150 could include one or moreoptical sensors that allow the measurement of blood constituents andrelated parameters, acoustic respiratory sensors, electrocardiographsensors, and the like.

More generally, the sensor assembly 150 can include one or more sensorsthat measure one or more of a variety of physiological parameters,including oxygen saturation, carboxyhemologbin (HbCO), methemoglobin(HBMet), fractional oxygen, total hemoglobin (HbT/SpHb), pulse rate,perfusion index, electrical heart activity via electrocardiography, andblood pressure. Other examples of physiological parameters that may bemeasured include respiratory rate, inspiratory time, expiratory time,inspiration-to-expiration ratio, inspiratory flow, expiratory flow,tidal volume, end-tidal CO₂ (ETCO₂), CO₂, minute volume, apnea duration,breath sounds, rales, rhonchi, stridor, changes in breath sounds such asdecreased volume or change in airflow, heart rate, heart sounds (e.g.,S1, S2, S3, S4, and murmurs), and changes in heart sounds such as normalto murmur or split heart sounds indicating fluid overload.

In some embodiments, the sensor assembly 150 can be an optical sensorhaving one or more emitters, such as light emitting diodes. The emittersmay emit multiple wavelengths of light that impinge on body tissue of aliving patient, such as a finger, foot, ear, or the like. The emittersmay also emit non-visible radiation. The sensor assembly 150 may furtherinclude one or more detectors that can receive light attenuated by thebody tissue of the patient. The detectors can generate physiologicalsignals responsive to the detected light. The sensor assembly 150 canprovide these physiological signals to the monitor 110 for processing todetermine one or more physiological parameters, such as certain of theparameters described above. An example of such a sensor assembly 150 isdescribed in U.S. Publication No. 2006/0211924, filed Mar. 1, 2006,titled “Multiple Wavelength Sensor Emitters,” the disclosure of which ishereby incorporated by reference in its entirety.

The cable 130 is connected to the sensor assembly 150 and to the monitor110. In some embodiments, the cable 130 includes two or more cables orcable assemblies, although it should be noted that the cable 130 canalso be a single cable 130. In the illustrated embodiment, the cable 130includes a sensor cable 112 and an instrument cable 114. The sensorcable 114 is connected directly to the sensor assembly 150 throughconnectors 133, 151, and the instrument cable 114 is connected directlyto the monitor 110 through a connector 131. The sensor cable 112 isconnected to the instrument cable 114 through connectors 135, 137.

In certain embodiments, the sensor cable 112 is a lightweight, flexiblecable used for a single medical patient and disposed of after use withthat patient. In contrast, the instrument cable 112 of certainembodiments is used for multiple patients and may be more durable thanthe sensor cable 112. For example, the instrument cable 112 may bethicker, stiffer, or heavier than the sensor cable 112. Advantageously,in certain embodiments, the lightweight, flexible characteristics of thesensor cable 112 make the sensor cable 112 more comfortable to attach toa patient. A patient with a sensor assembly 150 attached to her finger,for instance, could more easily move her hand with a lightweight sensorcable 112 attached to the sensor assembly 150. However, if some or allof the cable 130 were lightweight and flexible, it might be lessdurable. Hence, a portion of the cable 130 (e.g., the instrument cable114) is stronger and more durable, yet potentially heavier and lessflexible. The instrument cable 114 could therefore be used for multiplepatients, while the sensor cable 112 might be used for fewer patients,such as a single patient.

While the physiological monitor 110 of FIG. 1 is shown connecting to asingle sensor assembly 150, it may be advantageous in certainembodiments to connect to multiple sensors, such as sensors that monitordifferent physiological parameters. For instance, the physiologicalmonitor 110 could connect to a pulse oximetry sensor and an acousticsensor that measures respiratory rate, heart sounds, and relatedparameters. One way to provide multiple sensor functionality to thephysiological monitor 110 is to provide a splitter cable between themonitor and the cable 130 (see FIGS. 2 and 6). A splitter cable reducesor eliminates a need to build a second cable port into the chassis ofthe physiological monitor 110 to accommodate a second cable 130.Consequently, using a splitter cable can reduce costs. Moreover, using asplitter cable can reduce cross-talk noise between signal lines from thesensors.

However, as described above, upgrading the physiological monitor 110 toreceive input from multiple sensors using a splitter cable or the likecan create electrical shock hazards to the patient due to thepossibility of conductive paths forming through the sensors, cabling,and the patient. For example, if an acoustic sensor is placed on thechest and a defibrillator paddle touches the acoustic sensor, a surge ofcurrent could discharge through a conductive path formed in the patientbetween the acoustic sensor and a second sensor, and through thephysiological monitor 110. This current surge could injure the patientand damage the monitor 110.

Consequently, various embodiments of the cable 130 or an attachedsplitter cable can include one or more decoupling circuits (not shown)for reducing the risk of electric shock to the patient. Each decouplingcircuit can electrically decouple the sensor assembly 150 from themonitor 110 or can decouple multiple sensor assemblies 150. In additionto having its ordinary meaning, electrical decoupling can mean breakinga conductive path (e.g., by providing a dielectric between twoconductors) or increasing the resistance between conductors. Electricaldecoupling can be accomplished using transformers and/or optocouplers,as described below. The electrical decoupling of the decoupling circuitcan prevent or reduce harmful current surges from harming the patient.Example decoupling circuits are described below with respect to FIGS. 2through 6.

In addition to including decoupling circuitry in the cable 130 or in anattached splitter cable, it may be desirable to include other circuitryin the cable 130 or splitter cable. For example, the cable 130, asplitter cable, and/or the sensor assembly 150 may include one or moreinformation elements (not shown), which can be memory devices such asEEPROMs or the like. In one embodiment, the information element storescable management information, patient context information, and/orphysiological information. Example information elements are describedbelow with respect to FIGS. 6 through 14.

FIGS. 2A and 2B illustrate embodiments of physiological monitoringsystems 200A, 200B interfacing with multiple sensor assemblies 250. Thephysiological monitoring systems 200A, 200B each include a physiologicalmonitor 210, a splitter cable 220, two cables 230, and two sensorassemblies 250. The physiological monitoring systems 200A, 200B mayinclude all of the features of the physiological monitoring system 100described above.

In the physiological monitoring system 200A of FIG. 2A, a patientdecoupling circuit 240 a is provided in one of the cables 230 b. In thephysiological monitoring system 200B of FIG. 2B, the patient decouplingcircuit 240 b is provided in the splitter cable 220 b. These patientdecoupling circuits 240 a, 240 b can reduce or prevent ground loops fromforming in the patient and/or in the physiological monitoring system200. Although not shown, a decoupling circuit could instead be providedin one or both of the sensor assemblies 250.

The physiological monitor 210 processes and outputs physiologicalinformation received from sensors included in the sensor assemblies 250a, 250 b. The physiological monitor 210 of certain embodiments includesa power decoupling circuit 215, a processing board 217, and a connector219. The power decoupling circuit 215 may be a transformer or the likethat decouples power (e.g., AC electrical power) received from a powersource (such as an electrical outlet) and the circuitry of thephysiological monitor 210. The power decoupling circuit 215 prevents orsubstantially prevents current spikes from damaging the other componentsof the physiological monitor 210 or the patient. In embodiments wherethe physiological monitor 210 receives power from another source, suchas batteries, the power decoupling circuit 215 may not be included.

The processor 217 of certain embodiments is a microprocessor, digitalsignal processor, a combination of the same, or the like. The processor217 receives power from the power decoupling circuit 215. In someimplementations, the processor 217 processes physiological signalsreceived from the sensors 250 and outputs the processed signals to adisplay, storage device, or the like. In addition, the processor 217 maycommunicate with an information element (e.g., a memory device) includedin a cable or sensor. Information elements are discussed in greaterdetail below with respect to FIGS. 6 through 14.

The connector 219 includes a physical interface for connecting a cableassembly to the physiological monitor 210. In the embodiment shown inFIGS. 2A and 2B, a single connector 219 is provided. Additionalconnectors 219 may also be included in some implementations. Oneembodiment of a physiological monitor having additional connectors 219is described below with respect to FIG. 3.

The splitter cable 220 is provided in some embodiments to enable thephysiological monitor 210 having one connector 219 to interface withmultiple sensors 250. The splitter cable 220 interfaces with theconnector 219 through a monitor connector 221 in the splitter cable 220.In the depicted embodiment, where the splitter cable 220 interfaces withtwo sensors 250, cable sections 222 of the splitter cable 220, whichbranches into two sections generally forming a “Y” shape or the like.Thus, the splitter cable 220 can be a Y cable or the like. While thesplitter cable 220 is shown forming a “Y” shape, other configurationsand shapes of the splitter cable 220 may be used. For example, thesplitter cable 220 could branch into more than two cable sections 222 tointerface with more than two sensors 250.

The cable sections 222 are shown connected to the monitor connector 221and two cable connectors 223. In some embodiments, the cable sections222 branch into more than two parts and connect to more than two cableconnectors 223. In addition, in some embodiments the splitter cable 220couples directly to two or more sensors 250.

Some embodiments of the splitter cable 220 include one or more lines,conductors, or wires per cable connector 223. One line might beprovided, for example, to interface with one or more electrocardiograph(ECG) sensors. Two or three lines might be provided per cable connector223, for example, to interface with an optical or acoustic sensor. Forinstance, three lines might be provided, including a power line, asignal line, and a ground line (see FIGS. 4 and 5). The power linepowers the sensor 250, the signal line receives signals from the sensor250, and the ground line acts as an electrical return path for the powerand/or signal lines. In some embodiments, one or more of the linescoming from one sensor 250 a are placed at a predetermined distance fromone or more of the lines coming from another sensor 250 b to reducecross-talk interference between the sensors 250. One or moreelectromagnetic shielding and/or insulating layers may also be providedto help reduce cross-talk. Lines from different sensors may merge into ashared line that connects electrically to the monitor 210, and some formof multiplexing might be used to allow the different sensors tocommunicate along the shared lines.

The cables 230 a, 230 b interface with the splitter cable 220 in thedepicted embodiment through cable connectors 231. In certainembodiments, each cable 230 also includes a cable section 232 and asensor connector 233 that connects to a sensor 250. The cable section232 in some implementations includes one or more lines or wires forcommunicating with the sensor 250. For example, a power line, sensorline, and ground line may be provided that correspond to the power line,sensor line, and ground line in the example splitter cable 220 describedabove.

In an embodiment, one of the cables 230 includes the decoupling circuit240 a. In FIG. 2A, for example, the decoupling circuit 240 a is shown inthe cable section 232 of the cable 230 b. The decoupling circuit 240 amay also be placed in the cable connector 231 or the sensor connector233, or in a combination of one or more of the connectors 231, 233and/or the cable section 232. In another exemplary embodiment, FIG. 2Bshows that the decoupling circuit 240 b can be included in one of thecable sections 222 of the splitter cable 220 b. The decoupling circuit240 b may also be placed in the monitor connector 221 or the sensorconnector 223, or in a combination of the cable sections 222 and/or oneor more of the connectors 221, 223.

Multiple decoupling circuits 240 may also be provided in one or more ofthe cables 230 and/or in the splitter cable 220 in other embodiments. Inparticular, in one embodiment when N cables 230 are provided (or onesplitter cable 220 with N connectors 223), N−1 decoupling circuits 240are provided in N−1 of the cables 230 or in the various sections of thesplitter cable 220.

The decoupling circuit 240 of certain embodiments electrically decouplesa sensor 250 from the physiological monitor 210. In addition, thedecoupling circuit 240 can electrically decouple one sensor (e.g., thesensor 250 b) from another sensor (e.g., the sensor 250 a) in certainembodiments. The decoupling circuit 240 can be a transformer, anoptocoupler, a DC-DC converter, a switched-mode converter, or the likeor a combination of the foregoing. In addition, the decoupling circuit240 can include one or more optical fibers. An optical fiber may be usedin place of the signal line, for example. More detailed embodiments ofthe decoupling circuit 240 are described below with respect to FIGS. 4and 5.

The sensors 250 connect to the sensor connectors 233 of the cables 230.In an embodiment, one of the sensors 250 is an optical sensor, such as amultiple wavelength oximetry sensor. The other sensor 250 in oneembodiment is an acoustic sensor. In addition, the sensor 250 may be anacoustic sensor that also monitors ECG signals, such as is described inU.S. Provisional Application No. 60/893,853, titled “Multi-parameterPhysiological Monitor,” and filed Mar. 8, 2007, the disclosure of whichis hereby incorporated by reference in its entirety. Many other types ofsensors 250 can also be used to monitor one or more physiologicalparameters.

FIG. 3 illustrates another embodiment of a physiological monitoringsystem 300 having multiple cables 230. The physiological monitoringsystem 300 may have certain of the features of the physiologicalmonitoring systems 100, 200 described above. For example, like thephysiological monitoring system 200 described above, the physiologicalmonitoring system 300 includes a physiological monitor 310, two cables230, and two sensors 250. In the physiological monitoring system 300, adecoupling circuit 240 is provided in one of the cables 230 b.

Like the physiological monitor 210, the physiological monitor 310includes a power decoupling circuit 215 and a processor 217. Unlike thephysiological monitor 210, however, the physiological monitor 310includes two connectors 319 for interfacing directly with two cableswithout using a splitter cable. To save costs for users who will useonly one sensor 250 with the physiological monitor 310, a decouplingcircuit 240 is not provided in the physiological monitor 310. Instead,the decoupling circuit 240 can be provided in a separate cable 230 bthat can be used with the physiological monitor 310.

For example, a user might use one cable 230 a and sensor 250 a at a timewith the physiological monitor 310. Since only one sensor 250 a is beingused, ground or other current loops are less likely to form in thepatient. If the user later wishes to use additional sensors 250, theuser can obtain a cable 230 b having the decoupling circuit 240. Usingthe cable 230 b can beneficially allow the user to continue using thephysiological monitor 310 without performing an upgrade to thephysiological monitor's 310 internal components.

FIG. 4 illustrates another embodiment of a physiological monitoringsystem 400 having multiple cables 430. The physiological monitoringsystem 400 may have certain of the features of the physiologicalmonitoring systems 100, 200, 300 described above. For example, like thephysiological monitoring systems described above, the physiologicalmonitoring system 400 includes a physiological monitor 410, two cables430, and two sensors 450. The features described with respect to FIG. 4may also be applied to a monitoring system having a splitter cableinstead of multiple cables.

In the depicted embodiment, the cables 430 are shown connected to thephysiological monitor 410 and to the sensors 450. Connectors 419 in thephysiological monitor 410 couple with connectors 431 of the cables 430,and connectors 433 of the cables couple with connectors 451 of thesensors 450. A cable section 432 extends between the connectors 431, 433of each cable.

The cable 430 a includes a power line 462 a, a ground line 464 a, and asignal line 466 a extending from the connector 431 to the connector 433.These lines form electrical connections with corresponding power,ground, and signal lines in the connector 419 a of the physiologicalmonitor 410 and in the connector 451 a of the sensor 450 a. Likewise,the cable 430 b includes a power line 462 b, a ground line 464 b, and asignal line 466 b. These lines form electrical connections withcorresponding power, ground, and signal lines in the connector 419 b ofthe physiological monitor 410. In addition, these lines extend from theconnector 431 to a decoupling circuit 440. A power line 472, ground line474, and signal line 476 extend from the decoupling circuit 440 to theconnector 431 to form electrical connections with corresponding power,signal, and ground lines in the connector 451 b of the sensor 450 b. Thecable section 432 can also include one or more electrical insulation andshielding layers, materials, or fillers. Although not shown, one or moreof the cables 430 a, 430 b may also include one or more communicationslines for communicating with information elements.

In the depicted embodiment, the ground line 464 a is connected to theground line 464 b in the physiological monitor 410 through line 464 c.When both sensors 450 are placed on a patient, the ground lines 464 aand 474 b may also be in electrical communication through the patient,as illustrated by the dashed line 484. If the decoupling circuit 440were not present in one of the cables 430, a ground loop might be formedalong the lines 464 a, 464 b, 464 c, 474, and 484 (illustrated with boldlines) due to, for example, a difference in electrical potential in thelines 464 a, 464 b, 464 c, and 474. While not shown in bold, currentloops might also form in some cases among the power lines 462 a, 462 b,472 or the signal lines 466 a, 466 b, 476.

Advantageously, in certain embodiments, the decoupling circuit 440reduces the risk of a ground or other loop forming by decoupling one ormore of the power lines 462 b, 472, the signal lines 464 b, 474, or theground lines 464 b, 474. More detailed embodiments illustrating how thedecoupling circuit 440 could decouple one or more lines is describedbelow with respect to FIGS. 5A through 5C and FIG. 8C.

While only one decoupling circuit is shown, in other embodiments,multiple decoupling circuits may be provided in one cable 430. Forinstance, a first decoupling circuit could be connected to the powerline 462 b and the ground line 466 b, and a second decoupling circuitcould be connected to the signal line 464 b and to the ground line 466b. In addition, in certain embodiments, there may be a decouplingcircuit in each cable 430 a, 430 b.

FIG. 5A illustrates a more detailed embodiment of a decoupling circuit540 a suitable for use with any of the embodiments discussed herein. Thedecoupling circuit 540 a may include all the features of the decouplingcircuits 240, 340, and 440 described above. For example, the decouplingcircuit 540 a may be included in a medical cable assembly, such as asplitter cable, medical cable, or the like, or in a sensor assembly. Thedecoupling circuit 540 a can decouple electrical signals and prevent orreduce ground or other conducting loops from forming and can protectagainst current surges in a multi-sensor physiological monitoringsystem.

The decoupling circuit 540 a is shown within dashed lines. Thedecoupling circuit 540 a of various embodiments receives a signal line562 a, a power line 566 a, and a ground line 564 a. These lines can beconnected to a physiological monitor (not shown). In addition, thedecoupling circuit 540 a receives a signal line 572 a, a power line 576a, and a ground line 574 a, which may be connected to a sensor (notshown).

In an embodiment, the power line 566 a provides power from aphysiological monitor to the decoupling circuit 540 a, which providesthe power to the sensor through the power line 576 a. The signal line572 a provides a physiological signal from the sensor to the decouplingcircuit 540 a, which provides the physiological signal to the monitorthrough the signal line 562 a. The ground lines 564 a and 574 a act asreturn paths for their respective signal and power lines 562 a, 566 a,572 a, 576 a.

The decoupling circuit 540 a, in some implementations, includes anoptocoupler 542 a and a transformer 544 a. The optocoupler 542 areceives physiological signals from the sensor line 572 a and providesthe signals to the sensor line 562 a optically using, for example, aphotodiode 546 a and a phototransistor 548 a. Because the signals aretransmitted optically, in certain embodiments there is no electricalcontact between the signal lines 562 a, 572 a. Similarly, thetransformer 544 a provides power from the power line 566 a to the powerline 576 a without electrical contact between the lines 566 a, 576 a.Through mutual inductance, electromagnetic energy is transferred fromone winding 550 a of the transformer 544 a to another winding 552 a.Because the signals are transmitted using mutual inductance, there is noelectrical contact between the power lines 566 a, 576 a.

In certain embodiments, because the power lines 566 a, 576 a and signallines 562 a, 572 a are electrically decoupled, the ground lines 564 a,574 a can also be electrically decoupled. As shown, a ground line 543 aof the optocoupler 542 a on the monitor side connects to the ground line564 a, and a ground line 553 a of the optocoupler 542 a on the sensorside connects to the ground line 574 a. As a result, the risk of groundloops forming in the patient may be reduced or eliminated.

Many other configurations of the decoupling circuit 540 a may beemployed. For instance, a second optocoupler 542 a may be used in placeof the transformer 544 a, or a second transformer 544 a may be used inplace of the optocoupler 542 a. In addition, some forms of DC-DCconverters or switched mode converters may be used in place of eitherthe optocoupler 542 a or the transformer 544 a. Alternatively, one ormore optical fibers may be used.

Moreover, one or more optical fibers can be used instead of theoptocoupler 542 a or the transformer 544 a. Because the optical fiberstransmit optical, rather than electrical signals, using optical fibersin certain embodiments beneficially reduces the likelihood of groundloops forming in the patient. In one example embodiment, the optocoupler542 a in FIG. 5A is replaced with an optical fiber, but the transformer544 a is still included in the decoupling circuit 540 a. The opticalfiber allows signals to be transmitted through the signal line whilepreventing current from passing through the signal line. In addition, ifoptical fibers are used for the signal lines of multiple sensors, theoptical fibers can also reduce cross-talk interference among the signallines.

FIG. 5B illustrates an embodiment of a circuit 500B that includes adecoupling circuit 540 b. The decoupling circuit 540 b may include allthe features of the decoupling circuits 240, 340, and 440 describedabove. For example, the decoupling circuit 540 b may be included in amedical cable assembly, such as a splitter cable, medical cable, or thelike, or in a sensor assembly.

The decoupling circuit 540 b is shown decoupling a signal line 562 bconnected to a monitor from a signal line 572 b connected to a sensor.In the depicted embodiment, the decoupling circuit 540 b is an analogoptocoupler. The decoupling circuit 540 b includes a transmittingphotodiode 541 and two receiving photodiodes 545 a, 545 b for feedbackcontrol.

The transmitting photodiode 541 receives physiological signals from thesignal line 572 b via a feedback circuit 557 (described below). Thetransmitting photodiode 541 transmits the physiological signals to bothof the receiving photodiodes 545 a, 545 b. The receiving photodiode 545b transmits the signals it receives from the transmitting photodiode 541to the monitor via signal line 562 b. The receiving photodiode 545 atransmits the signals it receives to a feedback circuit 557.

Many diodes are inherently unstable due to nonlinearity and driftcharacteristics of the diodes. As a result of such instability, thesignal produced by the transmitting photodiode 541 may not correspond tothe signal provided by the signal line 572 b from the sensor. Thereceiving diode 545 a can therefore be used as a feedback diode toprovide a received signal to the feedback circuit 557.

The feedback circuit 557 can include an amplifier or the like thatadjusts its output provided to the transmitting photodiode 541 based atleast partly on a difference between the signal of the transmittingphotodiode 541 and the receiving diode 545 a. Thus, the feedback circuit557 can correct for errors in the transmitted signal via feedback fromthe feedback or receiving diode 545 a.

FIG. 5C illustrates another embodiment of a circuit 500C that includes adecoupling circuit 540 c. The decoupling circuit 540 c may include allthe features of the decoupling circuits 240, 340, and 440 describedabove. For example, the decoupling circuit 540 c may be included in amedical cable assembly, such as a splitter cable, medical cable, or thelike, or in a sensor assembly.

The decoupling circuit 540 c is shown decoupling a power line 566 cconnected to a monitor from a power line 576 c connected to a sensor.The decoupling circuit 540 c can be used together with the decouplingcircuit 540 b of FIG. 5B in some embodiments. For example, thedecoupling circuits 540 b, 540 c may be provided on the same circuitboard. Like the decoupling circuit 540 b, the decoupling circuit 540 cuses feedback to dynamically correct or control the output of thedecoupling circuit 540 c.

The decoupling circuit 540 c in the depicted embodiment is a flybacktransformer having two primary windings 550 c, 551 c and one secondarywinding 552 c. The primary winding 550 c receives power (VIN) from thepower line 566 c. A switched mode power supply 560 also receives power(VIN) from the power line 566 c. In an embodiment, the switched modepower supply 560 is a DC-DC converter or the like. A switch pin 562 ofthe power supply 560 can be enabled or otherwise actuated to allow power(VIN) to cycle through the primary winding 550 c. The switch pin 562 maycause the power to be switched according to a predetermined duty cycle.Feedback may be used, as described below, to maintain a stable orrelatively stable duty cycle.

As the primary winding 550 c is being energized, the primary winding 550c may store energy in itself and in a core 563 of the transformer.Through inductive coupling, this energy may be released into thesecondary winding 552 c and into the primary winding 551 c. The polarityof the windings 552 c, 551 c (as indicated by the dots on the windings)may be the same to facilitate the transfer of energy. Likewise, thepolarity of the windings 552 c, 551 c may differ from the polarity ofthe winding 550 c.

Like the feedback receiving photodiode 545 a described above, theprimary winding 551 c acts as a flyback winding in certain embodimentsto transmit the received power as a feedback signal. A rectifier 565rectifies the power received from the primary winding 551 c and providesa feedback power VFB to a feedback pin 566 of the power supply 560. Thepower supply 560 may then use the difference between the receivedfeedback power VFB and the transmitted power VIN to adjust VIN tocompensate for any error in the transmitted power. For example, thepower supply 560 can adjust the duty cycle described above based atleast partly on the error, e.g., by increasing the duty cycle if the VFBis low and vice versa. This flyback operation can advantageouslymaintain a stable or substantially stable power duty cycle despitevarying load conditions on the decoupling circuit 540 c.

The secondary winding 550 c can provide an output to a linear powersupply 570, which may rectify the received power, among other functions.The linear power supply 570 may provide the power to the power line 576c for transmission to the sensor.

FIGS. 6A and 6B illustrate an example splitter cable 620. FIG. 6Adepicts a side view of the splitter cable 620 while FIG. 6B depicts abottom view of the splitter cable 620. The splitter cable 620 includes ahousing 607 that includes a circuit board 640 having a decouplingcircuit, show in phantom. The housing 607 further includes wires 642,also shown in phantom, in communication with the circuit board 640 andwith first cable sections 630 a, 630 b and a second cable section 622 ofthe splitter cable 620. The housing 607 is also shown connected to thesecond cable section 622, which in turn connects to a connector 621. Inan embodiment, the connector 621 is used to connect the splitter cable620 to a physiological monitor.

The housing 607 of the splitter cable 620 further connects to one of thefirst cable sections 630 a through a connector 631. Another one of thefirst cable sections 630 b is integrally coupled to the housing 607 ofthe splitter cable 620 in the depicted embodiment. In oneimplementation, the splitter cable 620 and the cable 630 b are used toobtain physiological information from a single sensor, and the cable 630a may be added to the splitter cable 620 to obtain physiologicalinformation from an additional sensor. It should be noted that in analternative embodiment, the first cable section 630 b is not integrallyattached to the housing 607 but instead attaches to the housing using asecond connector. Or, both of the first cable sections 630 could beintegral to the housing 607.

The circuit board 640 interfaces with both first cable sections 630 a,630 b and with the second cable section 622. The circuit board 640 mayinclude, for example, one or more integrated circuits or discretecircuit components that together are implemented as a decouplingcircuit. In addition, the circuit board 640 can include one or moreinformation elements for storing various forms of data.

Turning to FIG. 7, additional embodiments of cable assemblies 730 willbe described. As explained above with respect to FIG. 1, cableassemblies having two separate cables may be provided in someembodiments. These separate cables can include a sensor cable 712 and aninstrument cable 714. In one embodiment, the sensor cable 712 is ashort, lightweight cable, adapted to facilitate comfortable attachmentof sensors to a medical patient. In certain embodiments, the instrumentcable 714 is a heavier, sturdier cable, acting as a durable interfacebetween the sensor cable 712 and a monitor. Sensor cables 712 andinstrument cables 714 may be periodically replaced. Periodic replacementis advantageous in certain embodiments for a wide variety of reasons.For example, the cable can become soiled or damaged, causing cablefailure, inaccurate results, or patient cross-contamination.

In addition, one or more decoupling circuits or information elements(see FIGS. 7 and 8) may be incorporated into the cable assembly 730 incertain embodiments. The information elements may store cable managementinformation related to usage of the cable assembly and devices connectedto the cable assembly. The information elements may also store patientcontext information related to patient identification and patientmovement (flow) among hospital departments, thereby tracking thepatient's progress throughout the hospital. Examples of patient contextinformation are described more fully in U.S. patent application Ser. No.11/633,656, titled “Physiological Alarm Notification System,” filed Dec.4, 2006, which is hereby incorporated by reference in its entirety.Moreover, the information elements can store physiological informationin some implementations.

Referring again to FIG. 7, a sensor cable 712 is shown connected to asensor assembly 750. The sensor cable 712 may include a flexible cablesection 732 having an elongated shape, a connector 751 for interfacingwith a sensor assembly 750, and a connector 737 for interfacing with aninstrument cable 714. The flexible nature of the cable section 732 inone embodiment is provided to enable greater patient comfort, as thepatient can move more easily with a flexible sensor cable 712 attached.

The depicted example instrument cable 714 includes a stiff or relativelyrigid, durable cable section 734 having an elongated shape, a connector735 for interfacing with the sensor cable 712, and a connector 731 forinterfacing with a physiological monitor. As the instrument cable 714 ofvarious embodiments is not connected directly to the patient, theinstrument cable section 734 may be less flexible (and more durable)than the sensor cable section 732, thereby extending the life of theinstrument cable 714.

Decoupling circuitry and/or information elements may be included withinthe sensor cable 712, the instrument cable 714, or both. The decouplingcircuits and/or information elements may be placed in any of theconnectors 737, 751, 735, or 731 or in either cable section 732, 734. Inother embodiments, one or more information elements may be included inany of the splitter cables described above. In alternative embodiments,the sensor cable 712 can be a splitter cable.

FIGS. 8A and 8B illustrate example layouts of a physiological monitoringsystem 800. FIGS. 8A and 8B illustrate various information elements 860,862, and 864. The information elements 860, 862, and 864 may be used tostore cable management information, patient context information, and/orphysiological information. Although not shown, the information elements860, 862, and 864 may also be used in the splitter cable embodimentsdescribed above. Moreover, decoupling circuitry may be included in thecables of FIGS. 8A and 8B.

Referring to FIG. 8A, a physiological monitoring system 800A includes aphysiological monitor 810 that communicates with a sensor 850 through aninstrument cable 814 and a sensor cable 812. An information element 860is included in the sensor cable 812.

The physiological monitor 810 interfaces with the instrument cable 814using a connector 819, which mates with a connector 831 of theinstrument cable 814. The instrument cable 814 mates in turn with thesensor cable 812 through a connector 835 on the instrument cable 814 anda corresponding connector 837 on the sensor cable 812. The sensor cable812 in turn connects to a sensor 850 through a connector 833 and acorresponding connector 851 on the sensor 850. In alternativeembodiments, the sensor cable 812 may be a splitter cable.

In the embodiment shown, the information element 860 is located in theconnector 837. Other placements for the information element 860 are alsopossible. For example, the information element 860 could be locatedanywhere in the sensor 850 or in the sensor cable 812, including in asensor cable section 832 or the connector 833. In addition, theinformation element 860 could also be located in the instrument cable814 instead, or two or more information elements 860 could be used, oneor more in each cable 812, 814 (see, e.g., FIG. 8).

The information element 860 can include any one or more of a widevariety of information elements. In an embodiment, the informationelement 860 is a non-volatile information element, such as, for example,an erasable programmable read-only memory (“EPROM”). “EPROM” as usedherein includes its broad ordinary meaning known to one of skill in theart, including those devices commonly referred to as “EEPROM “EPROM,” aswell as any types of electronic devices capable of retaining theircontents even when no power is applied and/or those types of devicesthat are reprogrammable. In an embodiment, the information element is animpedance value associated with the sensor, such as, for example, aresistive value, an impedance value, an inductive value, and/or acapacitive value or a combination of the foregoing. In addition, thecable's information element could be provided through an active circuitsuch as a transistor network, memory chip, flash device, or otheridentification device, including multi-contact single wire informationelements or other devices, such as those commercially available fromDallas Semiconductor or the like. Moreover, the information element maybe random access memory (RAM), read-only memory (ROM), or a combinationof the same.

In an embodiment, the physiological monitor 810 communicates with theinformation element 860 via a serial transmission line 840. In oneembodiment, the serial transmission line 840 is a multi-drop bus,although in alternative embodiments, the serial transmission line 840 isa 1-wire bus, a SCSI bus, or another form of bus. Once the physiologicalmonitor 810 determines that it is connected to the sensor cable 812, itsends and receives signals to and from the information element 860 toaccess cable management information and/or patient context information.Alternatively, the physiological monitor 810 does not access theinformation element 860 until requested to do so by a user (e.g., aclinician). In addition, the physiological monitor 810 may alsoautomatically access the information element 860 or access theinformation element 860 in response to a user request.

Cable management information that may be stored on the informationelement 860 may include information on cable usage, sensor usage, and/ormonitor usage. Cable usage data may include, for example, information onthe time the cable has been in use, enabling the physiological monitor810 to determine when the sensor cable 812 is near the end of its life.Sensor usage data may include, for example, information on what sensorshave been attached to the sensor cable 812, for how long, and the like.Similarly, monitor usage data may include, for example, information onwhat monitors have been attached to the sensor cable 812, for how long,and the like. More detailed examples of cable management information aredescribed below, with respect to FIG. 9.

Patient context information that may be stored on the informationelement 860 may include patient identification data and patient flowdata. In one example embodiment, patient identification data includes atleast the patient's name and one or more identification numbers. Patientflow data may include, for example, details regarding the departmentsthe patient has stayed in, the length of time therein, and devicesconnected to the patient. More detailed examples of patient contextinformation may also be found below, with respect to FIG. 9.

Advantageously, in certain embodiments, the physiological monitor 810uses the cable management information in various embodiments todetermine when to replace a cable in order to prevent cable failure. Thephysiological monitor 810 may also use the information element 860 totrack sensor 850 and physiological monitor 810 use. Some implementationsof the physiological monitor 810 enable the physiological monitor 810 totransmit some or all of the cable management information to a centralnurses' station or to a clinician's end user device, such as isdescribed in further detail below, with respect to FIG. 9. In someimplementations, the physiological monitor 810 or a central nurses'station sends an alarm to the end user device that alerts the user toimpending cable failure. For example, a clinician might receive an alarmnotification on a personal digital assistant (PDA), pager, or the like,which enables the clinician to replace the cable before it fails.Patient context information, including identification information, mayalso be provided along with the alarm to help the clinician identify thecable with the patient.

Moreover, the physiological monitor 810 may transmit some or all of thecable management information and/or patient context information to acentral server (see, e.g., FIG. 10). Inventory software on the centralserver can use this information to preemptively order new cables whencable inventory is low or at other times.

Different sensors 850 and physiological monitors 810 may be attached tothe same sensor cable 812. Thus, the cable management information mayalso include a list of which sensors 850 and physiological monitors 810have been attached to the cable 812, how long they were attached, andthe like. The physiological monitor 810 may also provide thisinformation to the central server to keep track of or journal thisinformation. The cable management information is therefore used in someembodiments to derive patient monitoring metrics, which may be analyzedto monitor or improve hospital operations. A hospital may use thesemetrics, for example, to determine when to replace cables or todetermine whether personnel are using the cables improperly or aredamaging the cables through improper use.

The patient context information in some embodiments also enables thesensor cable 812 to be identified with a particular patient. As thesensor cable 812 of some embodiments may be transported with the patientwhen the patient is moved about the hospital, when the sensor cable 812is attached to different monitors 850, the data stored in theinformation element 860 may be transferred to the new monitor 850. Thus,during the patient's stay at the hospital or at discharge, theinformation element 860 of certain embodiments has patient flow datathat a hospital can use to monitor or improve operations. The flow dataof multiple patients may be used, for instance, to determine the numberof patients staying in a particular department at a given time and theequipment used during those patients' stay. Knowing this information,the hospital can adjust equipment inventories and staff assignments tomore efficiently allocate hospital resources among the variousdepartments.

FIG. 8B illustrates another embodiment of a monitoring system 800B. Themonitoring system 800B preferably includes all the features of themonitoring system 800A and additionally includes an information element862 in the instrument cable 814 and an information element 864 in thesensor 850. The information elements 862, 864 may have the same ordifferent characteristics of the information element 860, including thesame or different memory type, capacity, latency, or throughput.

In an embodiment, the serial transmission line 840 connects thephysiological monitor 810 to the information element 860 in the sensorcable 812 as above. However, the serial transmission line 840 alsoconnects to the information elements 862, 864. The physiological monitor810 may therefore access the information elements 860, 862, 864 whilerunning generally few transmission lines 840.

The information elements 862, 864 may have all or a portion of thefunctionality of the information element 860. In one embodiment, thesame data is stored in each of the information elements 860, 862, 864,thereby providing data redundancy. Additionally, in such embodiments theinstrument cable 814 may stay with the patient as the patient moves fromone department to another, in place of or in addition to the sensorcable 812. Moreover, in one embodiment only the instrument cable 814 orthe sensor assembly 850 has an information element 862 or 864, and thesensor cable 812 does not have an information element 860.

The placement of the information elements 862, 864 can be in any of avariety of locations. For example, the information element 862 may belocated in either one or the connectors 831, 835 or in the instrumentcable section 834. Likewise, the information element 864 of the sensor850 may be located in the connector 851 or in another part of the sensor850.

Although not shown, the sensor cable 812 and/or the instrument cable 814may have multiple information elements in some embodiments. Whenmultiple information elements are used, certain data may be stored onsome information elements, and other data may be stored on others. Forinstance, cable management information may be stored on a separateinformation element from patient context information, and physiologicalinformation may be stored on yet another information element.

FIG. 8C illustrates an embodiment of a circuit 800C for facilitatingcommunication between a monitor and one or more information elements890. The circuit 800C may be included in any of the cable or sensorassemblies described above, including in a splitter cable, anon-splitter cable, an instrument cable, a sensor cable, a sensorassembly, combinations of the same, and the like. In addition, thecircuit 800C may be used in conjunction with the circuits 500B and 500Cin a single cable, e.g., on the same circuit board, or in combinationwith multiple cables and/or sensor assemblies.

Advantageously, in certain embodiments, the circuit 800C provideselectrical decoupling for communications lines 877, 879, 882, and 883,which provide communications between a monitor and one or moreinformation elements. In addition, the circuit 800C may provide sensorconnection status to a monitor via a sensor detect circuit 872.

A decoupling circuit 540 d shown includes digital decoupling logic toelectrically decouple one or more information elements and one or moresensors from the monitor. The decoupling circuit 540 d includestransformers on a chip and associated logic that perform digitaldecoupling. In one embodiment, the decoupling circuit 540 d is aADuM130x series chip from Analog Devices. In other embodiments,optocouplers and/or other transformers are used.

Communications lines 882, 883 allow the monitor to transmit and receivedata to and from one or more information elements 890. The line 882 is amonitor transmit line 882, and the line 883 is a monitor receive line883. Each of these lines 882, 883 is electrically decoupled from thecommunications line 877 by the decoupling circuit 540 d. Thecommunication lines 877, 879 may be electrically coupled with the one ormore information elements 890.

In an embodiment, the communications line 877 is a bus, such as a 1-wirebus. The communications line 877 may be used to both transmit andreceive data to and from the monitor. The communications line 879 may beused to receive data from the monitor. A MOSFET switch 876 or the likeis in communication with the depicted communications line 879, whichselectively transmits signals to the one or more information elements890.

The monitor receive line 883 is in communication with a power validationcircuit 878, which determines whether the feedback power VFB describedabove with respect to FIG. 5C is high enough. If the feedback power VFBis too low, the data received from the information elements 890 may notbe used because the data may be corrupt.

In the depicted embodiment, the power validation circuit 878 includes acomparator 889 that compares the feedback power VFB with a referencevoltage. If the feedback power VFB is equal to or higher than thereference voltage, the comparator 889 might output a high voltage. Thishigh voltage can be selectively overridden by a MOSFET switch 887 inresponse to communications received from the information elements 890.If the feedback power VFB is lower than the reference voltage, thecomparator 889 might output a low voltage. The low voltage can overridethe MOSFET switch 887 such that communications from the informationelements 890 are not sent to the monitor.

In the depicted embodiment, sensor connection status is provided to themonitor via the sensor detect circuit 872. The sensor detect circuit 872includes a sensor detect line 875 in communication with a pull-upresistor 873. When a sensor 885 is not connected to the line 875, theline 875 may be pulled high. This high voltage may be inverted by aMOSFET switch 874 to provide a low signal to the monitor via sensorconnect line 881. The switch 874 may be omitted in some embodiments.

In response to a sensor 885 being connected to the sensor detect line875, a shorted line 886 (or low resistance line) in the sensor 885 cancause the line 875 to be pulled low. This low value can be inverted bythe switch 874 to provide a high signal to the monitor. This signal canindicate that the sensor 885 is connected. Conversely, if the sensor 885is disconnected, the line 875 may again be pulled high, resulting in alow output of the switch 874. As a result, the monitor may receive arapid or near-immediate indication that the sensor 885 has beendisconnected.

The sensor detect circuit 872 also includes passive elements in thedepicted embodiment, such as a capacitor 891, to smooth or debouncecontact oscillations from the sensor 885. Thus, the sensor detectcircuit 872 can also be considered a debounce circuit. In otherembodiments, the sensor detect circuit 872 can be replaced with otherforms of debounce circuitry.

Advantageously, in certain embodiments, the sensor detect circuit 872can be used instead of polling the one or more information elements 890frequently to determine if the sensor 885 is connected. Alternatively,the polling cycle of the one or more information elements 890 may bereduced. Reducing or eliminating the polling cycle can reduce powerconsumption by the circuit 800C.

The sensor detect circuit 872 may be used to detect the connection ofcables, such as a splitter cable, as well as or instead of detectingsensor connections. In some embodiments, a sensor detect line 875 may beprovided for each sensor in a multi-sensor system, each cable, or thelike. Moreover, the sensor detect circuit 872 may also be used withcables that do not have a decoupling circuit.

FIG. 9 illustrates a block diagram of example forms of data that can bestored on an information element. In the depicted embodiment, patientcontext information 920, cable management information 930, andphysiological information 940 are shown. The patient context informationcan include patient identification data 922 and patient flow data 924.Cable management information 930 can include cable usage data 932,sensor usage data 934, and instrument usage data 936. However, while thedata is depicted in FIG. 9 as comprising discrete categories, data fromone category may be included within another. Data from one or morecategories also may not be included, or alternatively, additional datacategories than that shown may be included.

Turning to more specific examples, in one embodiment patientidentification data 922 can include a patient's name, a patient's uniquehospital identification number, type of patient or body tissue,information about the patient's age, sex, medications, and medicalhistory, and other information that can be useful for the accuracy ofalarm settings and sensitivities and the like. In addition, the patientidentification data 922 may also include an SpO₂ fingerprint, determinedby a pulse oximeter. In one such embodiment, the SpO₂ fingerprint isdetermined by calculating a ratio of an infrared detected wavelength anda red detected wavelength. The SpO₂ fingerprint can be used to detect ifa sensor or cable is being improperly reused.

Patient flow data 924 can include a record of departments the patienthas visited, length of stay (LOS) in those departments, overall LOS inthe hospital, admittance date and time, discharge date and time, timestamps for events occurring in the hospital, and the like. Some or allof this information, in conjunction with the patient identificationdata, can constitute a patient flow profile.

Cable usage data may include buyer or manufacturer information, cabletype, serial number of the cable, date of purchase, time in use, andcable life monitoring functions (CLM), including near expirationpercentage, update period, expiration limit, and an index of functions.In addition, the cable usage data 932 may include numerous read writeparameters, such as the number of times the cable is connected to amonitoring system, the number of times the cable has been successfullycalibrated, the total elapsed time connected to a monitor system, thenumber of times the cable has been connected to one or more sensors, thetotal time used to process patient vital parameters, the cumulativecurrent, voltage, or power applied to the cable, the cumulativetemperature of the cable, and the expiration status of the cable.

In an embodiment, the number of times the cable is placed on or removedfrom a patient is monitored and an indication is stored in the memory.The number of times a sensor connected to the cable is placed on orremoved from a patient can be monitored by monitoring the number ofprobe off conditions sensed, or it can be monitored by placing aseparate monitoring device on the cable or sensor to determine when asensor clip is depressed, opened, removed, replaced, attached, or thelike.

In an embodiment, the average operating temperature of the cable ismonitored and an indication stored. This can be done, for example,through the use of bulk mass or through directly monitoring thetemperature of the cable or the temperature of the cable's connectors.In an embodiment, the number of different monitors connected to thecable is tracked and an indication is stored in memory. In anembodiment, the number of times the cable is calibrated is monitored,and an indication is stored in memory. In an embodiment, the number ofpatients that use a cable is monitored and an indication is stored. Thiscan be done by, for example, by storing sensed or manually enteredinformation about the patient and comparing the information to newinformation obtained when the cable is powered up, disconnected and/orreconnected, or at other significant events or periodically to determineif the cable is connected to the same patient or a new patient. In anembodiment, a user is requested to enter information about the patientthat is then stored in memory and used to determine the useful cablelife. In an embodiment, a user is requested to enter information aboutcleaning and sterilization of the cable, and an indication is stored inthe memory. Although described with respect to measuring certainparameters in certain ways, various other electrical or mechanicalmeasurements can be used to determine any useful parameter in measuringthe useful life of a cable.

Sensor usage data 934 can include some or all of the same information asthe cable usage data but applied to sensors attached to the cable, andmay also include information on the type or operation of the sensor,type or identification of a sensor buyer, sensor manufacturerinformation, sensor characteristics including the number of wavelengthscapable of being emitted, emitter specifications, emitter driverequirements, demodulation data, calculation mode data, calibrationdata, software such as scripts, executable code, or the like, sensorelectronic elements, sensor life data indicating whether some or allsensor components have expired and should be replaced, encryptioninformation, monitor or algorithm upgrade instructions or data, or thelike. In an embodiment, the sensor usage data 934 can also includeemitter wavelength correction data.

Sensor usage data 934 can also include the number of emitting devices,the number of emission wavelengths, data relating to emission centroids,data relating to a change in emission characteristics based on varyingtemperature, history of the sensor temperature, current, or voltage,emitter specifications, emitter drive requirements, demodulation data,calculation mode data, the parameters it is intended to measure (e.g.,HbCO, HbMet, etc.) calibration data, software such as scripts,executable code, or the like, sensor electronic elements, whether it isa disposable, reusable, or multi-site partially reusable, partiallydisposable sensor, whether it is an adhesive or non-adhesive sensor,whether it is reflectance or transmittance sensor, whether it is afinger, hand, foot, forehead, or ear sensor, whether it is a stereosensor or a two-headed sensor, sensor life data indicating whether someor all sensor components have expired and should be replaced, encryptioninformation, keys, indexes to keys or has functions, or the like monitoror algorithm upgrade instructions or data, and some or all of parameterequations.

Instrument usage data 936 can include buyer or manufacturer information,information on the type of monitors that the cable has connected to,number of monitors the cable has connected to, duration of cableconnections to the monitors, duration of use of the monitor, trendhistory, alarm history, sensor life, an identification number for aspecific monitor, and the like. In addition, the instrument usage data936 may include all or a portion of all the cable and sensor usage datadescribed above.

The physiological information 940 may include any of the physiologicalparameters described above, obtained from the sensors or monitorsattached to the information element 960. In one implementation, theinformation element 960 enables the physiological information 940 to betransferred between physiological monitors. As a result, a historicalview of the patient's physiological parameters may be provided todifferent monitors throughout the hospital. Thus, clinicians indifferent departments can observe the patient's physiologicalinformation obtained in a previous department, enabling clinicians toprovide a higher quality of care.

FIG. 10 illustrates an embodiment of a physiological monitoring system1000 which may be used in a hospital, nursing home, or other locationwhere medical services are administered (collectively “hospital”).Certain aspects of the physiological monitoring system 1000 aredescribed in more detail in U.S. patent application Ser. No. 11/633,656,titled “Physiological Alarm Notification System,” filed Dec. 4, 2006,which is hereby incorporated by reference in its entirety.

The physiological monitoring system 1000 of certain embodiments includespatient monitoring devices 1002. The patient monitoring devices 1002 ofvarious embodiments include sensors 1050, one or more physiologicalmonitors 1010, cables 1030 attaching the sensors 1050 to the monitors1010, and a network interface module 1006 connected to one or morephysiological monitors 1010. Each patient monitoring device 1002 in someembodiments is part of a network 1020 of patient monitoring devices1002. As such, the patient monitoring devices 1002 in these embodimentscan communicate physiological information and alarms over a hospitalwireless network (WLAN) 1026 or the Internet 1050 to clinicians carryingend user devices 1028, 1052.

The network interface module 1002 of certain embodiments transmitsphysiological information on demand or in the event of an alarm to theend-user devices 1028, 1052 and/or transmits the alarm to a centralnurses' station. Alternatively, the network interface module 1002transmits information and alarms to a server 1036. The server 1036 is acomputing device, such as an appliance server housed in a data closet ora workstation located at a central nurses' station. The server 1036passes the information or alarms to the end user devices 1028, 1052 orto the central nurse's station. The alarms may be triggered when certainphysiological parameters exceed safe thresholds, thereby enablingclinicians to respond rapidly to possible life-threatening situations.Situations giving rise to an alarm might include, for example, decreasedheart rate, respiratory rate, low SpO₂ levels, or any otherphysiological parameter in an abnormal range.

The network interface module 1002 in one embodiment also performs cablemanagement by generating an alarm when one of the cables 1030 is nearingthe end of its life. The network interface module 1002 determineswhether the cable's 1030 life is close to expiring by, for example,analyzing some or all of the data described above with respect to FIG.9. In one embodiment, if the network interface module 1002 determinesthat the cable life is close to expiration, the network interface module1002 provides an expiration message as an alarm.

In one embodiment, the server 1036 receives this expiration message. Theserver 1036 then checks an inventory stored in a database 1038 to see ifa replacement cable is available. If there is no replacement cable inthe inventory, the server may forward the message to a supplier 1070over the Internet 1050 (or through a WAN, leased line or the like). Inan embodiment, the server 1036 transmits an email message to a supplier1070 that indicates the cable location, cable condition, and/or othercable usage data. The supplier 1070 in one embodiment is a cable seller.Upon receiving the message, the supplier 1070 may automatically ship anew cable to the hospital. Consequently, cable 1030 inventories are ableto be maintained with minimal or no user intervention in thisimplementation, and cables 1030 may be replaced preemptively, beforecable failure.

In additional embodiments, the network interface module 1006 may monitorsensor utilization, such as the number of sensors used during thepatient's stay, the types of sensors, and the length of time in usebefore replacement. Such data can be used by the hospital topreemptively plan restocking and set department par inventory levels. Inaddition, a supplier can use this data to restock the hospital orimplement a just in time inventory control program. Moreover, suchinformation can be used by the supplier to improve overall cablereliability and for the hospital to better plan and manage consumables.

The network interface module 1006 of various implementations alsoperforms context management. In one embodiment, context managementincludes associating context information with physiological informationto form a contextual data package. As described above, contextinformation may include patient identification data and patient flowdata. In addition, context information may include context informationrelated to usage of the network interface module 1006 and contextinformation related to the network. For example, this additional contextinformation may include an identification number of the networkinterface module 1006, time stamps for events occurring in thephysiological monitoring system 1000, environmental conditions such aschanges to the state of the network and usage statistics of the networkinterface module 1006, and identification information corresponding tothe network (e.g., whether the network connection is WiFi or Ethernet).

The network interface module 1006 receives context information in oneembodiment by a nurse entering the information in the network interfacemodule 1006 or from the server 1036. The network interface module 1006transmits or communicates the contextual data package to cliniciansduring an alarm, upon clinician request, or on a scheduled basis. Inaddition, the network interface module 1006 may transmit a continuousstream of context information to clinicians.

The server 1036 receives contextual data packages from a plurality ofnetwork interface modules 1006 and stores the contextual data package ina storage device 1038. In certain embodiments, this storage device 1038therefore archives long-term patient data. This patient data may bemaintained even after the patient is discharged. Thus, contextinformation may be stored for later analysis to, for example, developpatient care metrics and improve hospital operations. The patient datacould be deleted after the care metrics are developed to protect patientprivacy.

Although the functions of cable management and context management havebeen described as being performed by the network interface module 1006,in certain embodiments, some or all of these functions are insteadperformed by the physiological monitor 1010. In addition, thephysiological monitor 1010 and the network interface module 1006 mayboth perform cable management and/or context management functions.

FIG. 11 illustrates an embodiment of a usage tracking method 1100 fortracking the life of a medical cable. In one implementation, the usagetracking method 1100 is performed by the network interface module and/orone of the physiological monitors described above. More generally, theusage tracking method 1100 may be implemented by a machine having one ormore processors. Advantageously, in certain embodiments, the usagetracking method 1100 facilitates replacing a cable prior to failure ofthat cable.

The usage tracking method 1100 begins by obtaining sensor parametersfrom a sensor at block 1102. At block 1104, cable usage informationstored in an information element is tracked. The cable usage informationcan be tracked by at the same time or substantially the same time asobtaining sensor parameters from the sensor. Alternatively, the cableusage information may be tracked by determining cable usage at the startor end of monitoring (e.g., obtaining sensor parameters), orperiodically throughout monitoring. In addition, the cable usageinformation may be tracked even if the block 1102 were not performed,e.g., when the monitor is not currently obtaining parameters from thesensor.

At decision block 1106, it is determined whether the cable's life isclose to expiring (or whether the cable has in fact expired). Thisdetermination may be made using the data described above with respect toFIG. 9. In addition, the this determination may be made using sensorlife functions applied analogously to the life of the cable.

If it is determined that the cable life is close to expiration (or hasexpired), an expiration message is provided at block 1108. In oneembodiment, this message is provided as an alarm on the monitor or at acentral nurses' station. The message may also be provided to aclinician's end user device, which may be located in the hospital or ata remote location. Moreover, the message may be provided to a server,which forwards the message to a supplier, which ships a new cable. In anembodiment, the message is an email that indicates the cable location,cable condition, and/or other cable usage data. If, however, it isdetermined that the cable life is not close to expiration (or is notexpired), the usage tracking method 1100 loops back to block 1102 tocontinue monitoring. In effect, the usage tracking method 1100 maycontinue monitoring and/or tracking cable usage information until thecable is close to expiration or has expired.

FIG. 12 illustrates an embodiment of a cable inventory method 1200 forcontrolling cable inventory. The cable inventory method 1200 may beperformed by a server, such as the server 1038 described above. Moregenerally, the cable inventory method 1200 may be implemented by amachine having one or more processors. In one embodiment, the method1200 is performed in response to the method 1100 providing an expirationmessage at step 1108.

At block 1202, an expiration message is received from a monitor,indicating that a cable is close to expiration or has expired. At block1204, an inventory is checked for a replacement cable. This inventorymay be a hospital inventory, a record of which may be maintained in ahospital database or the like.

If it is determined at decision block 1206 that there is no replacementcable in the inventory, a new cable is ordered automatically to order aat block 1208. In an embodiment, this block 1208 is performed byelectronically contacting a supplier to order the cable, for example, bysending a request over a network such as the Internet. Consequently, incertain embodiments, the cable inventory method 1200 enables the cableto be replaced preemptively, before cable failure. If, however, there isa replacement cable in inventory, the cable inventory method 1200 ends.However, in alternative embodiments, the cable inventory method 1200orders a replacement cable regardless of the inventory, such that apredetermined level of cable inventory is maintained.

In additional embodiments, the cable inventory method 1200 may monitorsensor utilization, such as the number of sensors used during thepatient's stay, the types of sensors, and the length of time in usebefore replacement. Such data can be used by the hospital topreemptively plan restocking and set department par inventory levels. Inaddition, a supplier can use this data to restock the hospital orimplement a just-in-time program. Moreover, such information can be usedby the supplier to improve overall cable reliability, and for thehospital to better plan and manage consumables.

FIG. 13 illustrates an example context management method 1300 formanaging patient context. In an embodiment, the context managementmethod 1300 is performed by a physiological monitor, such as any of themonitors described above. More generally, certain blocks of the contextmanagement method 1300 may be implemented by a machine having one ormore processors. The context management method 1300, in certainembodiments, advantageously enables a patient to be assigned a cablewith a unique identifier upon the first connection of the cable to thepatient or to a monitor.

At block 1300, a cable is connected to a monitor, for example, by aclinician such as a nurse. Thereafter, a temporary patient ID isassigned to the cable at block 1304. The temporary ID may beautomatically assigned when power is provided to the information elementin the cable, or a prompt may be provided to a clinician, who thenassigns the ID. In addition, the temporary ID may also be previousstored on the cable. The temporary patient ID enables the cable to beidentified as uniquely relating to the patient, prior to the patient'sidentification information being provided to the cable. The temporarypatient ID may be stored in the information element of the cable.

At block 1306, patient flow data is stored in the information element.The patient flow data may include flow data described above with respectto FIG. 9. For example, the patient flow data may include informationregarding connected devices, a department ID associated with the cable,and time spent by the cable in a department. By storing patient flowdata, the context management method 1300 can enable the flow of thepatient may be monitored upon connection of the cable to a monitor.Thus, even if the nurse neglects to identify the cable with the patient,the cable can have data indicating when it is being used on the same ora different patient.

At decision block 1308 it is determined whether a real patient ID hasbeen provided. If so, then the temporary ID is replaced with the realpatient ID at block 1310. The real patient ID may include any of thepatient identification information described above, with respect to FIG.13. If, however, it is determined that a real patient ID has not beenprovided, the context management method 1300 loops back to block 1306 tocontinue storing patient flow data in the information element.

FIG. 14 illustrates another example context management method 1400 formanaging patient context. In an embodiment, the context managementmethod 1400 is performed by one or more monitors, such as any of themonitors described above. More generally, certain blocks of the contextmanagement method 1400 may be implemented by a machine having one ormore processors.

At block 1402, a cable is connected to a monitor. In one embodiment,this block is performed by a clinician, such as a nurse. Patient flowdata is then stored in an information element at block 1404. The patientflow data may include the flow data described above with respect to FIG.9.

At decision block 1406, it is determined whether the cable has beenconnected to a new monitor. If it has, patient flow data is transferredfrom the cable to the new monitor at block 1408. In an embodiment, thenew monitor determines whether the cable has been connected to the newmonitor. Alternatively, the cable makes this determination. Transferringthe patient flow data to the new monitor provides, in certainembodiments, the advantage of enabling the monitor to know where thepatient has been in the hospital and for how long. If a new monitor hasnot been connected, the context management method 1400 ends.

Those of skill in the art will understand that information and signalscan be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that can be referenced throughout theabove description can be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill will further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans can implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of this disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein can be implementedor performed with a machine, such as a general purpose processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general purpose processor can be amicroprocessor, processor, controller, microcontroller, state machine,etc. A processor can also be implemented as a combination of computingdevices, e.g., a combination of a DSP and a microprocessor, a pluralityof microprocessors, one or more microprocessors in conjunction with aDSP core, or any other such configuration. In addition, the term“processing” is a broad term meant to encompass several meaningsincluding, for example, implementing program code, executinginstructions, manipulating signals, filtering, performing arithmeticoperations, and the like.

The steps of a method or algorithm described in connection with theembodiments disclosed herein can be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module can reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, a DVD, or any other form of storage medium known in the art. Acomputer-readable storage medium is coupled to the processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium can reside in anASIC. The ASIC can reside in a user terminal. In the alternative, theprocessor and the storage medium can reside as discrete components in auser terminal.

The modules can include, but are not limited to, any of the following:software or hardware components such as software object-orientedsoftware components, class components and task components, processes,methods, functions, attributes, procedures, subroutines, segments ofprogram code, drivers, firmware, microcode, circuitry, data, databases,data structures, tables, arrays, and/or variables.

In addition, although certain inventions have been disclosed in thecontext of certain embodiments, it will be understood by those skilledin the art that the inventions disclosed herein extend beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the inventions and obvious modifications and equivalentsthereof. In particular, while the system and methods have been describedin the context of certain embodiments, the skilled artisan willappreciate, in view of the present disclosure, that certain advantages,features and aspects of the acoustic signal processing system, device,and method may be realized in a variety of other applications andsoftware systems. Additionally, it is contemplated that various aspectsand features of the inventions disclosed herein can be practicedseparately, combined together, or substituted for one another, and thata variety of combination and subcombinations of the features and aspectscan be made and still fall within the scope of the inventions disclosedherein. Furthermore, the systems described above need not include all ofthe modules and functions described in certain embodiments. Thus, it isintended that the scope of the inventions disclosed herein disclosedshould not be limited by the particular disclosed embodiments describedabove, but should be determined only by the claims that follow.

What is claimed is:
 1. A pulse oximetry system for reducing the risk ofelectric shock to a medical patient, the pulse oximetry systemcomprising: a plurality of physiological sensors, at least one of thephysiological sensors comprising: a light emitter configured to impingelight on body tissue of a living patient, the body tissue includingpulsating blood, and a detector responsive to the light afterattenuation by the body tissue, wherein the detector is configured togenerate a signal indicative of a physiological characteristic of theliving patient; and a splitter cable comprising: a monitor connectoroperative to connect to a physiological monitor, a plurality of sensorconnectors each operative to connect to one of the physiologicalsensors, a plurality of cable sections each disposed between a sensorconnector and the monitor connector, each of the cable sectionscomprising one or more electrical conductors, the one or more electricalconductors for at least some of the cable sections comprising: a powerline configured to supply power to one or more of the plurality ofphysiological sensors; a signal line configured to transmit thephysiological signals from one or more of the physiological sensors tothe physiological monitor; and a ground line configured to provide anelectrical return path for the power line; and one or more decouplingcircuits in communication with selected ones of the one or moreelectrical conductors, the one or more decoupling circuits configured tocommunicate physiological signals between one or more of thephysiological sensors and the physiological monitor, the one or moredecoupling circuits operative to electrically decouple the physiologicalsensors from each other, wherein the one or more decoupling circuits areconfigured to prevent ground loops from forming in the ground line. 2.The pulse oximetry system of claim 1, wherein the one or more decouplingcircuits comprise an optocoupler in communication with the signal line.3. The pulse oximetry system of claim 1, wherein the one or moredecoupling circuits comprise a flyback transformer in communication withthe power line.
 4. The pulse oximetry system of claim 1, wherein atleast one of the one or more decoupling circuits comprises a digitaldecoupling circuit.
 5. The pulse oximetry system of claim 1, wherein theplurality of physiological sensors comprise an acoustic sensor.
 6. Amedical apparatus for reducing the risk of electric shock to a medicalpatient when used with a pulse oximeter, the apparatus comprising: aplurality of physiological sensors, at least one of the physiologicalsensors comprising: a light emitter configured to impinge light on bodytissue of a living patient, the body tissue including pulsating blood,and a detector responsive to the light after attenuation by the bodytissue, wherein the detector is configured to generate a signalindicative of a physiological characteristic of the living patient; asplitter cable operative to connect the plurality of physiologicalsensors to a physiological monitor, the splitter cable comprising aplurality of cable sections each comprising one or more electricalconductors configured to interface with one of the physiologicalsensors; and one or more decoupling circuits disposed in the splittercable, the one or more decoupling circuits being in communication withselected ones of the one or more electrical conductors, the one or moredecoupling circuits configured to communicate physiological signalsbetween one or more of the physiological sensors and the physiologicalmonitor, the one or more decoupling circuits operative to electricallydecouple the physiological sensors from each other.
 7. The apparatus ofclaim 6, wherein the one or more decoupling circuits comprise one ormore of an optocoupler, a transformer, and an optical fiber.
 8. Theapparatus of claim 6, wherein the one or more decoupling circuitscomprise one decoupling circuit disposed in a monitor connector of thesplitter cable.
 9. The apparatus of claim 6, wherein the one or moredecoupling circuits comprise a plurality of decoupling circuits disposedin sensor connectors of the splitter cable.
 10. The apparatus of claim6, wherein the plurality of decoupling circuits are disposed in all butone of the cable sections.
 11. The apparatus of claim 6, wherein theplurality of physiological sensors comprise an optical sensor and anacoustic sensor.
 12. The apparatus of claim 6, further comprising asensor detect circuit configured to provide an indication of aconnection status of one of the sensors without polling the sensor. 13.The apparatus of claim 6, wherein one or more of the cable sectionscomprise a power line configured to supply power to one of thephysiological sensors, a signal line configured to transmit thephysiological signals from the physiological sensor to the physiologicalmonitor, and a ground line configured to provide an electrical returnpath for the power line.
 14. The apparatus of claim 13, wherein the oneor more decoupling circuits are configured to substantially preventground loops from forming in the ground line.
 15. A method of reducingthe risk of electric shock to a medical patient as used with a pulseoximeter, the method comprising: providing a plurality of physiologicalsensors, at least one of the physiological sensors comprising a lightemitter configured to impinge light on body tissue of a medical patientand a detector configured to generate a signal indicative of aphysiological characteristic of the living patient responsive to thelight after attenuation by the body tissue; providing a medical cableassembly comprising one or more electrical conductors configured toallow communication between the plurality of physiological sensors and aphysiological monitor, such that the medical cable assembly is operativeto provide signals representing physiological information of a medicalpatient from the plurality of physiological sensors to the physiologicalmonitor; and electrically decoupling the plurality of physiologicalsensors from each other using one or more decoupling circuits disposedin the medical cable assembly, the one or more decoupling circuits beingin communication with the plurality of physiological sensors and withthe physiological monitor.
 16. The method of claim 15, wherein the oneor more decoupling circuits comprise an optocoupler.
 17. The method ofclaim 15, wherein the one or more decoupling circuits comprise atransformer.
 18. The method of claim 15, further comprising providing anindication of a connection status of one of the sensors without pollingthe sensor.
 19. The method of claim 15, wherein providing the medicalcable assembly further comprises providing at least one sensor cableconfigured to be coupled with at least one of the physiological sensorsand at least one instrument cable configured to be coupled with the atleast one sensor cable and with the physiological monitor.
 20. Themethod of claim 15, wherein the medical cable assembly comprises asplitter cable.